Reduced output topology for multi-reference switching amplifiers

ABSTRACT

A method and attendant circuitry reduces the number of regulatory and switching devices in a multi-reference switching amplifier. In the preferred embodiment, multiple independently-modulated effective references are summed at a load through use of both linear and switched control of switching devices.

REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/406,207, filed Aug. 27, 2002, the entire content of which isincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to multi-reference switching amplifiersand, in particular, to a simplified output topology associated with suchamplifiers.

BACKGROUND OF THE INVENTION

Multi-reference switching amplifiers of the type shown, for example, inPCT application PCT/US99/26691, entitled “Multi-Reference High AccuracySwitching Apparatus,” yield significantly higher instantaneousresolution than standard switching amplifiers. The cost for thisperformance improvement, however, resides in an additional regulatorydevice and one or two switching devices (for non-bridged or bridgedconfigurations, respectively) per reference added.

Particularly in cost-sensitive applications, there remains a need for asimplified output topology that retains the function and resolutioninherent in multi-reference switching amplifiers.

SUMMARY OF THE INVENTION

The present invention resides in a method and attendant circuitry forreducing the number of regulatory and switching devices in amulti-reference switching amplifier. In the preferred embodiment,multiple independently-modulated effective references are summed at aload through use of both linear and switched control of switchingdevices.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, switching devices 125, 126, 127, and 128 form abridged output known in the art as an “H” bridge. Inductors 129 and 130,in conjunction with capacitor 131, filter switching alias products fromthe load 132. Note that in this case only four output switching devicesare used.

Data separator 101 isolates coarse data 102 and fine data 103 fromincoming data stream 100. These data streams 102 and 103 are presentedas inputs to pulsewidth modulators 104 and 105, which proportionallyconvert said coarse data 102 and fine data 103 into modulated coarsepulse stream 133 and fine pulse stream 134, respectively. If the sign106 of the incoming data stream 100 is high, as indicated by dataseparator 101, switching device 125 is modulated by the coarsepulsewidth stream 133, through AND gate 107. While the sign 106 is high,transmission gate 109 is activated, forcing the control input ofswitching device 126 to follow the complement of coarse pulse widthstream 133, as inverted by inverter 121. Resistor 119 serves to limitoutput current of differential amplifier 111.

Conversely, if the indicated sign 106 of the incoming data stream 110 islow; switching devices 127 and 128 are modulated by the coarsepulsewidth stream 133 (through AND gate 108) and its complement (throughtransmission gate 110 and inverter 121), respectively. Resistor 120serves to limit output current of differential amplifier 112. Coarsemodulation in this fashion operates exactly as shown in themulti-reference application referenced above.

A second reference voltage, proportional to the power supply voltage V+,is formed by the resistor divider 123/124, and input to differentialamplifiers 111 and 112. When not disturbed by transmission gate 109,switching device 125, or diode 115, differential amplifier 111 outputs avoltage to cause the output of switching device 126 to equal thereference voltage formed by resistors 123 and 124. When the indicatedsign 106 is low, NOR gate 113 turns on diode 115 with the inverse (frominverter 135) of the fine pulsewidth stream from pulsewidth modulator105, forcing switching device 126 to turn on, through the resultantoutput increase of differential amplifier 111. This results in switchingat the output of switching device 126 between ground and the referencevoltage formed by resistors 123 and 124, inversely modulated byfine-resolution 103 provided to pulse width modulator 105.

When not disturbed by transmission gate 110, switching device 127, ordiode 116, differential amplifier 112 outputs a voltage to cause theoutput of switching device 128 to equal the reference voltage formed byresistors 123 and 124. When the indicated sign 106 is high, NOR gate 114turns on diode 116 with the inverse (from inverter 135) of the finepulse width stream from pulse width modulator 105, forcing switchingdevice 128 to turn on, through the resultant output increase ofdifferential amplifier 112. This results in switching at the output ofswitching device 128 between ground and the reference voltage formed byresistors 123 and 124, inversely modulated by fine-resolution 103provided to pulse width modulator 105.

In the discussion above, coarse-resolution data 102 is used to modulateV+ on one side of load 132, while fine-resolution data 103 is used tomodulate the reference voltage formed by resistors 123 and 124 on theother side of load 132, under control of data sign 106. Althoughsummation at the load of multiple references, modulated by appropriateresolutions, directly follows the technique disclosed in themulti-reference application referenced above, note that this isaccomplished by the present invention with significantly fewer outputswitching devices.

1. In a multi-reference switching amplifier wherein switching devicescontrol power supplied to a load in response to an input data streamhaving a sign, a simplified output topology, comprising: first andsecond independently modulated references, wherein the second one of thereferences is derived through a voltage divider; a data separatoroperative to separate the input data stream into coursecoarse-resolution data and fine-resolution data; circuitry formodulating the first one of the references on one side of the load as afunction of the coarse-resolution data; and circuitry for modulatingsecond one of the references on the other side of the load as a functionof the fine-resolution data.
 2. The simplified output topology of claim1, wherein the first one of the references is a supply rail.
 3. In amulti-reference switching amplifier, wherein switching devices controlpower supplied to a load, a circuit comprising: first and secondindependently modulated references, wherein the second independentlymodulated reference is derived through a voltage divider; a dataseparator operative to separate an input data stream intocoarse-resolution data and fine-resolution data; a first circuitconfigured to modulate the first independently modulated reference on afirst side of the load as a function of the coarse-resolution data; anda second circuit configured to modulate the second independentlymodulated reference on a second side of the load as a function of thefine-resolution data.
 4. The circuit of claim 3, wherein the firstindependently modulated reference comprises a supply rail.
 5. Thecircuit of claim 3, wherein the first circuit and the second circuiteach comprise a pulsewidth modulation circuit.
 6. The circuit of claim3, wherein the first circuit is configured to modulate the firstindependently modulated reference on the first side of the load as afunction of the coarse-resolution data in response to the input datastream having a first sign, and wherein the first circuit is furtherconfigured to modulate the second independently modulated reference onthe first side of the load as a function of the fine-resolution data inresponse to the input data stream having a second sign.
 7. The circuitof claim 6, wherein the second circuit is configured to modulate thesecond independently modulated reference on the second side of the loadas a function of the fine-resolution data in response to the input datastream having the first sign, and wherein the second circuit is furtherconfigured to modulate the first independently modulated reference onthe second side of the load as a function of the coarse-resolution datain response to the input data stream having the second sign.
 8. Thecircuit of claim 7, wherein the first circuit comprises a firstplurality of switching devices and the second circuit comprises a secondplurality of switching devices.
 9. The circuit of claim 8, wherein thedata separator is further configured to couple a sign of the input datastream to the first and second circuits.
 10. The circuit of claim 9,wherein the first and second circuits each comprise a transmission gateconfigured to receive the sign of the input data stream, wherein eachrespective transmission gate is coupled to one of the respectiveswitching devices, and wherein each respective transmission gate isconfigured to provide the coarse-resolution data to the respectiveswitching device in response to the sign of the input data stream.
 11. Amethod for controlling a multi-reference switching amplifier configuredto supply power to a load, the method comprising: separating an inputdata stream into coarse-resolution data and fine-resolution data;dividing a first reference voltage to obtain a second reference voltage;modulating the first reference voltage on a first side of the load as afunction of the coarse-resolution data; and modulating the secondreference voltage on a second side of the load as a function of thefine-resolution data.
 12. The method of claim 11, wherein both said actsof occur in response to the input data stream having a first sign, andwherein the method further comprises: modulating the second referencevoltage on the first side of the load as a function of thefine-resolution data; and modulating the first reference voltage on thesecond side of the load as a function of the coarse-resolution data. 13.The method of claim 11, further comprising converting thecoarse-resolution data and the fine-resolution data into respectivepulsewidth modulated pulse streams.
 14. The method of claim 11, whereinsaid modulating the first reference voltage comprises switching thefirst side of the load between the first reference voltage and ground,and wherein said modulating the second reference voltage comprisesswitching the second side of the load between the second referencevoltage and ground.
 15. The method of claim 11, wherein said modulatingthe first reference voltage comprises using the coarse-resolution datato control a switching device coupled to the first side of the load. 16.The method of claim 11, wherein said modulating the second referencevoltage comprises using the fine-resolution data to control a switchingdevice coupled to the second side of the load.
 17. A multi-referenceswitching amplifier configured to supply power to a load, the amplifiercomprising: a first plurality of switching devices configured to coupleto a first side of the load; a second plurality of switching devicesconfigured to couple to a second side of the load; first and secondindependently modulated references, wherein the second independentlymodulated reference is derived through a voltage divider; a dataseparator operative to separate an input data stream intocoarse-resolution data and fine-resolution data; a first circuit coupledto the first plurality of switching devices and configured to modulatethe first independently modulated reference as a function of thecoarse-resolution data; and a second circuit coupled to the secondplurality of switching devices and configured to modulate the secondindependently modulated reference as a function of the fine-resolutiondata.
 18. The amplifier of claim 17, wherein, in response to the datainput stream having a first sign, the first circuit is configured tomodulate the first independently modulated reference as a function ofthe coarse-resolution data and the second circuit is configured tomodulate the second reference as a function of the fine-resolution data,and wherein, in response to the input data stream having a second sign,the first circuit is further configured to modulate the second referenceas a function of the fine-resolution data and the second circuit isfurther configured to modulate the first reference as a function of thecoarse-resolution data.
 19. The amplifier of claim 18, wherein the dataseparator is further configured to couple the sign of the input datastream to the first and second circuits.
 20. The amplifier of claim 18,wherein the first and second circuits each comprise a transmission gateconfigured to receive the sign of the input data stream, wherein eachrespective transmission gate is coupled to one of the respectiveswitching devices, and wherein each respective transmission gate isconfigured to provide the coarse-resolution data to the respectiveswitching device in response to the sign of the input data stream.